Quantification of VWF-specific antibodies. Humanized anti-VWF IgG and IgM chimeric monoclonal antibodies were used to establish standard curves to detect anti-VWF Ig antibodies. T3 VWD Ab⁺ IgG titers from 1:25 to 1:800 had a range of 2 to 135 A.U., whereas the higher titer positive controls reached over 1000 A.U. anti-VWF IgG. The single IgM-positive type 3 VWD with a low titer of 1:25 measured at 43 A.U. anti-VWF IgM. Symbols represent plasma samples and are differentiated into IgG (●) and IgM (■).